1. Field of Invention
This invention relates to building roof edge systems, specifically to the fascia cover, coping cover or other such roof edge cover of a fascia assembly, gravel stop assembly, coping assembly or other such building component assembly.
2. Discussion of Prior Art
Conventionally roof edge systems are intended to provide aesthetic roofing termination and waterproof along the perimeter of a flat or nearly flat roof. However, conventional roof edge systems are not aerodynamically configured, adversely affecting not only their performance under the action of wind, but also the performance of other parts or components of the roof under wind action, for example, wind action resulting from hurricanes, tornadoes or winter storms.
Prior Art FIGS. 1A and 1B show examples of the most common shapes of fascia covers presently used on roof edge systems. An abrupt change of surface slopes at the top arris of the fascia cover renders conditions for the generation of wind-induced vortices over the roof edge system and the roof at large, due to extremely high local airflow speed at the arris and inevitably severe flow separation from the downstream surface, a phenomenon that is inherent to such an abrupt slope change. Vortices create strong uplift forces that prove to be the prime cause of roof failures during high winds. Vortices also scour or sweep up roofing material, such as roof gravel or paver, which becomes a major source of wind-borne debris impacting and damaging adjacent structures.
Prior Art FIG. 2 shows a common shape of coping cover used on roof edge parapet walls. Similarly, the abrupt change of surface slopes at the outer top arris renders conditions for the generation of wind-induced vortices and strong uplift forces.
A handful of existing roof edge systems have elements that are intended for purposes other than aerodynamic ones but lead to some improvement in the aerodynamics of a roof edge system; however, lacking of a systematic aerodynamic design, they are of distance from being aerodynamically advanced, optimal or complete, each having identifiable flaws or disadvantages. Prior Art FIG. 3 shows a roof edge construction as disclosed in U.S. Pat. No. 4,780,999 to Webb and Hickman (1988). While intended for resilient anchoring, the shape of the fascia cover aerodynamically improves over that shown in Prior Art FIG. 1 because of reduction in abruptness of slope changes; however, the reduction is not sufficient to avoid high local airflow speed and large scale flow separation at the upper ridge of the fascia cover so that sizable vortices will inevitably occur above the inwardly and downwardly sloping portion as well as over the roof surface downstream. Another example of roof edge construction is shown in Prior Art FIG. 4 as disclosed in U.S. Pat. No. 4,598,507 to Hickman (1986) and also in U.S. Pat. No. 4,549,376 to Hickman (1986). The still abrupt slope changes, particularly at the upper front edge, make the shape of the fascia cover aerodynamically faulty. Prior Art FIG. 5 shows a coping assembly as disclosed in U.S. Pat. No. 6,212,829 B1 to Webb et. al. (2001). While intended for improved longitudinal alignment between adjacent coping covers, the cross-sectional shape of the coping cover is also aerodynamically improved over the more common shape shown in Prior Art FIG. 2, in light of mitigating vortex formation over the top face portion of the fascia cover; however, the blunt shape of the underside of the outer protruding cap portion, which forms a right angle with the wall, increases upward wind pressure load due to flow stagnation on the underside of the outer cap portion. This high pressure will also potentially be transmitted to the inside chamber of the coping cover due to any imperfect air tightness between the cover""s lower edge and the wall surface, pressurizing the inside chamber and resulting in undesired additional upward load on the top horizontal portion and outward force on the outer cap portion. In addition, these increased pressures will impose a stronger force to press rainwater present in the vicinity of the coping cover""s lower edge upwards into the cover""s chamber, exposing the internal components to wetting problems which the coping cover were supposedly to protect them from. This undermines the roof edge system""s functionality as a waterproof component for the building even under less severe wind conditions. Moreover, such an outward protruding shape, having a large protrusion depth relative to its vertical dimension, along with a blunt underside shape, will also induce strong wind suction on the outermost exterior surface of the coping cover, added to the outward force due to the internal pressurization mentioned above, pulling it outward away from the wall. This action in turn worsens the scenario of any imperfect air and water tightness and increases internal pressurization. Such a potential chain action in a positive feedback mode, severely increases the chances of wind induced damage and forced water-infiltration under high winds. Prior Art FIG. 6 shows the shape of the outer part of an Overly Manufacturing Company""s coping cover (date unknown), which also has a blunt lower cap portion, and has a large outward-protrusion depth. This configuration has similar faults as described for that in Prior Art FIG. 5. In addition, this configuration has a larger curvature on the front upper cap portion, which is more in favor of flow separation and vortex formation.
Prior Art FIG. 7 shows a fascia assembly as disclosed in U.S. Pat. No. 3,187,464 to Sharp (1965). While designed to provide a smooth appearing front exposed side, the rounded shape of the top ridge portion of the fascia cover slightly improves the fascia cover""s aerodynamics over an otherwise sharp top arris shape; nevertheless, the curvature of the top ridge or hump is too large, or its radius is too small with respect to the overall size of the fascia cover, making it effectively equivalent to an abrupt or sharp change in surface slope.
A detail review of the prior art reveals a reality that none of the existing roof edge systems or designs is aerodynamically configured to effectively mitigate wind-induced vortices affecting roof edge systems and roof zones adjacent to the edge. According to one of the roof edge manufacturers, MM Systems Corporation, Inc., nearly 75% of all incidents of roof blow-off occur at the roof edge (http://www.advanced-roofing.com/productservices/mmsc.htm, as of Nov. 16, 2000). In a news article related to the American National Standards Institute""s approval of Wind Design Standard for Edge Systems Used with Low Slope Roofing, it was claimed that 90% of the damage begins with wind and water leaks at the roof edge (Southern Building magazine, January/February, 1999). An Institute for Business and Home Safety article, Performance of Metal Building in High Winds, depicts that xe2x80x9chigh winds have peeled roof coverings back from roof edges like a metal key peels open a can of sardinesxe2x80x9d. Many other publicly available post-disaster survey data show that flat or nearly flat roof construction is one of the most wind-vulnerable structures and majority of the wind-induced damages start from the roof edge. In response to such a reality, American Society of Civil Engineers"" Standard ASCE 7-98 xe2x80x9cMinimum Design Loads for Buildings and Other Structuresxe2x80x9d, as a national standard, specifies significantly higher wind loads on edge zones (including corners) of a roof than any other part of a building for structural strength requirement. Also nearly all official building codes observed within various jurisdictions of the United States and other countries, including IBC, SBC, UBC, BOCA, FBC, SFBC and NBC, have similarly stringent provisions for the roof edge zones.
Clearly, there is an urgent need in the industry and marketplace for aerodynamically advanced, systematically and coordinately configured roof edge systems to reduce wind actions on both the edge system and the edge zones of a roof While strengthening a structure has been, and continues to be, one of the solutions for safer roofs, a more physically fundamental solution is indeed to reduce the wind actions or the wind-induced forces themselves on the structure by using aerodynamic passive flow control methods as described in the present invention. While new constructions must be designed to meet the structural strength requirements stipulated by various building codes, incorporating an aerodynamic roof edge system instead of a conventional one will provide double protection to achieve safer roof and building constructions. For wind resistant retrofits of existing buildings, replacing a conventional roof edge system with an aerodynamic roof edge system will be more economical than replacing or renewing a roof structure or even a part of a roof structure, since the aerodynamic method will cost significantly less material and labor, and does not necessitate temporary removal of occupants and contents or interruption of business, and thus is more cost-effective.
In accordance with the present invention, aerodynamic roof edge systems comprise a streamlined or nearly streamlined fascia cover, coping cover or other such roof edge cover, of which slope changes between adjacent surfaces are systematically and coordinately controlled, reducing the intensity and size of wind-induced vortices generated at the roof edge and over the roof edge zone that potentially cause damage to the roof edge system and the roof in general.
Accordingly, several objects and advantages of the present invention are:
to provide roof edge systems which minimize the chance of damage to roof edge systems under severe wind conditions, and thus safeguard the integrity of a roof structure;
to provide roof edge systems which also reduce wind-induced uplift load on other parts of the roof, protecting them from windstorm damage;
to provide roof edge systems which reduce vortex scouring of roofing materials, such as roof gravel, paver or other ballast, and prevent them from becoming wind-borne missiles injuring people and damaging adjacent building envelopes during windstorms;
to provide roof edge systems which minimize accumulated displacement of roof gravel, paver or other ballast by moderate recurring winds, securing their functionality of protecting sheet membrane underneath from solar rays and wind uplift damage;
to provide roof edge systems which stabilize wind flow over the roof edge system and other parts of a roof structure under moderate but frequently recurring wind conditions, thus reduce high-frequency cycling fatigue loads on these components and increase their service life;
to provide roof edge systems which possess the desired aerodynamic performance to secure their conventional aesthetic and waterproofing functionality under both extreme and recurring weather conditions.
Further objects or advantages are to provide roof edge systems which retain all the original functions of a roof edge system, and which are still among the simplest, inexpensive to manufacture and convenient to install. These and still further objects and advantages will become apparent from a consideration of the ensuing description and drawings.